Speaking the Same (Chemical) Language

The organic chemistry course I teach makes use of a problem-solving website built on MarvinSketch to collect and evaluate student responses. This feature of the course has the awesome effect of forcing students and instructors to “speak the same language” when it comes to chemical structures and reaction mechanisms. The letters of our alphabet, so to speak, are the atoms, bonds, and curved arrows provided by the software. Since we all use the same software, and it doesn’t allow certain nonsensical drawings (such as a curved arrow pointing to nothing) a lack of clarity in student responses has become almost a non-issue.

For organic chemistry courses relying on paper and pencil, it’s very important for instructors to be clear about the drawing conventions and standards to which they expect students to adhere. As a former grader of mountains of orgo exams, I can profess that nonsensical errors and ambiguity are the most common sources of confusion for graders (and lost points for students). But it doesn’t have to be this way! With just a few words and illustrative examples, instructors can make their standards clear and help students avoid “nonsense errors.” If we tell our students the syntax and grammar of our chemical language and communicate our expectations, we can expect students to speak that language.

I’ve prepared an example of a list of these kinds of standards for my own use. Feel free to adapt it for use in your own courses (but a nod to the blog would be nice :-D).

Standards for Drawing Organic Reaction Mechanisms



  1. Timely and useful post. One of the major complaints I hear from students who do OWLS is that the software has a hard time recognizing what they are drawing. Half the battle is communication! Another problem is getting a list like this in front of the eyes of students.

    It would be nice to have a common set of conventions for arrow drawing – there’s still some disagreement as to how to draw them (e.g. – do “heads” that form bonds go to the atom or do they go between the two atoms where the bond forms?)
    One quibble: the “tails” in some of the examples you drew would ideally have lone pairs drawn (for instance when neutral oxygen is the nucleophile).


    1. Quack, I am inconsistent with lone pairs. Those are the kinds of inconsistencies in my approach that I wish students would see. 🙂

      I think every orgo professor has some unique riffs on mechanism drawing, and that’s a good thing to an extent (it’s nice to have your own style). Then again, students sometimes get the idea that they can use their own rationality-defying styles…


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